A locale is composed of several locale categories, see Aspects. When a program looks up locale dependent values, it does this according to the following environment variables, in priority order:
LC_xxx, according to selected locale category:
Variables whose value is set but is empty are ignored in this lookup.
LANG is the normal environment variable for specifying a locale.
As a user, you normally set this variable (unless some of the other variables
have already been set by the system, in /etc/profile or similar
LC_MESSAGES, and so on, are the environment
variables meant to override
LANG and affecting a single locale
category only. For example, assume you are a Swedish user in Spain, and you
want your programs to handle numbers and dates according to Spanish
conventions, and only the messages should be in Swedish. Then you could
create a locale named ‘sv_ES’ or ‘sv_ES.UTF-8’ by use of the
localedef program. But it is simpler, and achieves the same effect,
to set the
LANG variable to
es_ES.UTF-8 and the
LC_MESSAGES variable to
sv_SE.UTF-8; these two locales come
already preinstalled with the operating system.
LC_ALL is an environment variable that overrides all of these.
It is typically used in scripts that run particular programs. For example,
configure scripts generated by GNU autoconf use
LC_ALL to make
sure that the configuration tests don't operate in locale dependent ways.
Some systems, unfortunately, set
LC_ALL in /etc/profile or in
similar initialization files. As a user, you therefore have to unset this
variable if you want to set
LANG and optionally some of the other
LANGUAGE variable is described in the next subsection.